1. Technical Field
The present invention relates to a sensor ring used for detection of rotation of a rotating element and a method of manufacturing such a sensor ring.
2. Background Art
In general, a sensor ring is employed to detect rotation of a rotating element such as an axle of an automobile. The sensor ring has a cylindrical body mounted on the rotating element, an annular member extending from the cylindrical body in a radial direction of the cylindrical body and a plurality of openings formed in the annular member. These openings are spaced from each other in the circumferential direction of the annular member at constant pitches. A tooth is defined between each two adjacent openings of the annular member. The sensor ring is mounted on the rotating element such as an automobile axle, and a proximity sensor is provided nearby. The proximity sensor detects the teeth of the sensor ring which rotate with the rotating axle. The sensor ring and the proximity sensor in combination detect the rotational speed of the rotating element.
The sensor ring is generally press fitted over an outer periphery of a free end of the rotating element, and the free end of the rotating element has a stepwise portion in its outer periphery to receive the sensor ring. Specifically, the stepwise portion at the free end portion of the rotating element has an axially extending cylindrical surface to engage with an inner diameter portion of the cylindrical body of the sensor ring and a radially extending annular stop surface to support one end face of the sensor ring. The sensor ring is press fitted over the free end of the rotating element in the axial direction of the rotating element until it contacts the stop surface. The sensor ring seats on the radial stop surface of the rotating element so that the sensor ring is accurately positioned in the axial direction of the rotating element.
The cylindrical body of the sensor ring defines a center bore having a simple cylindrical surface to be fitted over the cylindrical surface of the stepwise free end portion of the rotating element.
The axially extending cylindrical surface and radially extending stop surface of the stepwise free end portion of the rotating element are formed by machining, and connection between these two surfaces is defined by an arcuate surface formed by a round nose of a cutting tool.
If a radius of the round nose of the cutting tool is relatively large, i.e., if the connection surface between the axially extending surface and radially extending surface of the rotating element has a relatively large radius of curvature, the end face of the sensor ring cannot abut on the stop surface of the rotating element when the sensor ring is press fitted over the rotating element. In such a case, positioning of the sensor ring in the axial direction of the rotating element and posture of the sensor ring relative to the stop surface (i.e., flatness of the sensor ring) are both unstable.
Even if the radius of the connection between the axial and radial surfaces of the free end portion of the rotating element is sufficiently small and the end face of the sensor ring can seat on the stop surface of the rotating element, the end face of the sensor ring may be deformed upon collision against the stop surface of the rotating element if the pressing force to press fit the sensor ring over the rotating element is excessively id great or If the press fitting operation is performed in an impacting way. This results in reduction of length of the sensor ring in the axial direction of the rotating element and causes instability in the axial position and horizontal posture of the sensor ring.
In order to press fit the sensor ring on the rotating element in a desired manner, it is ideal that the sensor ring is made from a one piece material having high stiffness and rigidity so that the sensor ring does not deform during the press fitting operation. Conventionally, the sensor ring is manufactured by sintering or machining. However, these manufacturing processes are complicated and troublesome. To simplify the manufacturing process, a press molding process is employed. A metallic plate material is press molded to a one piece product, but any conventional press molding method provides satisfactory products.
The present invention was conceived to eliminate the above described problems.
One object of the present invention is to provide a novel sensor ring which can always abut on the radial stop surface formed at the free end portion of the rotating element regardless of the size of connection curvature between the radial and horizontal surfaces of the free end portion of the rotating element and a manufacturing method of such a sensor ring.
Another object of the present invention is to provide a novel sensor ring which does not deform when it is press fitted over the free end portion of the rotating element and a manufacturing method of such a sensor ring.
Still another object of the present invention is to provide a novel sensor ring which is a one piece product manufactured from a plate material with high rigidity and a method of making the same.
Yet another object of the present invention is to provide a novel sensor ring which can be manufactured with a relatively small pressing force and a manufacturing method for such a sensor ring.
Still another object of the present invention is to provide a novel sensor ring which can suppress a manufacturing error and and a manufacturing method therefor.
According to one aspect of the present invention, there is provided a sensor ring of a type to be coaxially mounted on a free end portion of a rotating element for detecting rotations of the rotating element, the free end portion defining an axially extending cylindrical surface and a stop surface radially extending from the cylindrical surface for mounting the sensor ring thereon, characterized in that the sensor ring has a cylindrical portion which defines a cylindrical center opening to be press fitted over the axially extending cylindrical surface of the free end portion of the rotating element, and has a flange portion which extends radially outward from one end periphery of the cylindrical portion at an obtuse angle and abuts on the stop surface of the free end portion of the rotating element when the sensor ring is completely mounted on the rotating element.
Since the flange portion of the sensor ring extends diagonally outward in a radial direction from the periphery of the cylindrical portion of the sensor ring and has a gradually increasing diameter, the flange portion can avoid (or does not contact) a connection curvature between the axial and radial surfaces of the free end portion of the rotating element during the press fitting operation. As a result, the free end of the flange portion of the sensor ring can always abut on the radial stop surface of the rotating element. Thus, it is possible to locate the sensor ring on the rotating element at a desired position with desired flatness.
The flange portion of the sensor ring may have a chamfered inner surface to avoid the connection curvature between the axial and radial surfaces of the free end portion of the rotating element.
The free end of the flange portion may have a planar area which is parallel to the stop surface of the rotating element so that the flange portion of the sensor ring plane contacts the planar radial stop surface of the rotating element.
The sensor ring may have an annular sensing portion extending radially outward from the other end periphery of the cylindrical portion and an outer ring portion extending axially toward the flange portion from the outer periphery of the sensing portion to partly surround the cylindrical portion. The sensor ring is a one piece product having the cylindrical portion, the flange portion, the sensing portion and the outer ring portion.
A plurality of rectangular or square openings may be formed in the sensing portion at constant intervals in the circumferential direction of the sensor ring. Each of the openings may have a radially outer side which is furthest from the center of the sensor ring, a radially inner side which is closest to the center of the sensor ring, and two other sides connecting ends of the outer side with ends of the inner sides respectively. A radial position of the inner side of each opening may substantially be the same as that of the outer wall of the cylindrical portion of the sensor ring. The radial position of the outer side of the opening may substantially be the same as that of the inner wall of the ring portion.
According to another aspect of the present invention, there is provided a method of manufacturing a sensor ring from a blank of single plate material, the sensor ring blank including a cylindrical portion, a sensing portion extending radially outward from one end periphery of the cylindrical portion and an outer ring portion extending axially toward the other end periphery of the cylindrical portion from the outer periphery of the sensing portion to partly surround the cylindrical portion, characterized in that the blank is set on a lower metallic mold of the first mold unit with the sensing portion being directed downward (i.e., toward the lower mold) and the cylindrical portion being engaged with a nest plate provided on the lower mold, a presser mold is lowered toward the lower mold until it is received in a space defined by the cylindrical portion, sensing portion and outer ring portion so that the sensing portion is clamped between the presser mold and lower mold and the blank is held in position, a plurality of pierce punches are lowered toward the lower mold with downward movement of the pierce punches being guided by the presser mold to make a plurality of rectangular or square openings in the sensing portion at constant pitches in the circumferential direction of the sensing portion (piercing step), the blank is then removed from the lower mold of the first mold unit and set on a lower mold of the second mold unit with the inner wall of the cylindrical portion being supported by a first nest pin, the downwardly directed face of the sensing portion being supported by a stationary punch and the outer wall of the cylindrical portion being supported by a movable mold such that an upper length of the cylindrical portion slightly projects upward from the movable mold, an upper mold punch is lowered to sandwich the projecting length of the cylindrical portion between the upper mold punch and the movable mold thereby bending the projection length diagonally radially outward to form a flange portion of the sensor ring. Accordingly, the sensor ring having the flange portion is obtained.
By this manufacturing method, it is possible to make a sensor ring with high rigidity from a single plate material.
The pierce punches may be arranged with twice the pitch of the openings of the sensing portion so that the openings of the sensing portion are formed by first and second piercing operations. Between the first and second piercing operations, the blank may be rotated by one pitch of the sensing portion openings.
The lower mold of the first mold unit may have a plurality of bores (punch holes) to receive the pierce punches respectively. A second nest pin may be provided in the lower mold between two predetermined punch holes such that it is projectable from the upper surface of the lower mold. The nest pin may be pushed back and may not project during the first piercing operation. When the first piercing operation is finished and the blank is rotated by one pitch of the openings, the nest pin may project and fit in one of the pierced openings. Thus, positioning of the blank before the second piercing operation is accurately performed. Such a nest pin may be provided more than once. Recesses (or pin holes) for receiving the nest pins may be formed in the lower mold. Each of the nest pins may have a sharp free end. Each of the pin holes may have an oval cross section with its major axis extending in a radial direction of the sensor ring so that the nest pin holes are larger than the punch holes in the radial direction.
Each of the pierce punches may have a rectangular or square cross section and the presser mold may have mating rectangular or square grooves to slidably engage with and guide the pierce punches.
The upper mold punch of the second mold unit may have a lower smaller diameter portion to push down the first nest pin when the upper mold punch is lowered, an upper larger diameter portion for bending the projecting length of the cylindrical portion of the blank in a radially outward direction, and a C (chamfered) surface formed at a connection between the smaller and larger diameter portions. The smaller diameter portion may be in slide contact with the inner wall of the cylindrical portion of the sensor ring blank when the upper mold punch is moved downward.
The projecting length of the cylindrical portion may be determined to have a size such that the corner defined by a horizontal end face of the projecting length and the vertical inner wall of the cylindrical portion is collapsed by the lower surface of the large diameter portion of the upper mold punch.
The movable mold may have a vertically cylindrical surface which is exposed to and surrounds the peripheral wall of the small diameter portion of the upper mold punch when the upper mold punch is lowered, a horizontal annular surface which is exposed to the annular lower surface of the large diameter portion of the upper mold punch outside the C surface and a tapered surface which is exposed to the C surface of the upper mold punch and connects the vertical surface with the horizontal surface.
The tapered surface of the movable mold may be steeper than the C surface.
The length of the tapered surface may be about one half of that of the C surface in the radial direction of the sensor ring and the height of the tapered surface may be more than that of the C surface.
Additional objects, benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the following detailed description of the preferred embodiments and the appended claims as taken in conjunction with the accompanying drawings.